Fibrillated strand



H. BLADES ETAL 3,081,519

FIBRILLATED STRAND March 19, 1963 3 Sheets-Sheet 1 F I G. 2

Filed Jan. 31, 1962 FIG. I

FIG. 4a

FIG. 5

FIG-4b INVENTORS HERBERT BLADES JAMES RUSHTON WHITE BY 0( I77] ATTORNEYMarch 19, 1963 H. BLADES ETAL 3,081,519

FIBRILLATED STRAND Filed Jan. 31, 1962 3 Sheets-Sheet 2 FIG-7 FIG. 0 m[725 I x :544... I

I HERBERT BLADES JAMES RUSHW BY i I 'ITORNEY INVENTOR 5 March 19, 1963H. BLADES ETAI.

FIBRILLATED STRAND 3 Sheets-Sheet 3 Filed Jan. 51, 1962 FIG. l2

INVENTORS ll'll'llllnlll'lnll-lll 0 EZEzmoz 5132" E'W 5 HERBERT BLADESUnited States Patent 3,081,519 FIBRILLATED STRAND Herbert Blades,Wilmington, and James Rushton White, Chadds Ford, Del., assignors to E.I. du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware Filed Jan. 31, 1962, Ser. No. 170,182 21 Claims. (Cl. 28-81)This invention relates to a new process for shaping fiber-formingpolymers and the novel multi-fibrous strands thereby produced.

Synthetic polymers in fluid form can be directly converted into solidfibrous products by various procedures. Exemplary of such methods arethe conventional extrusion through multi-hole spinnerets of polymersolutions, polymer melts, plasticized polymer compositions, and reactivepolymer precursors; spray gun methods wherein air jets or electricalfields are made to attenuate a stream of fluid polymer; shearprecipitation methods; and others.

in general, those procedures which can directly produce multi-filament,yarn-like strands of adequate uniformity and texture for textilesusually require critical process control and afford relatively lowproductivity. Thus, for example, conventional spinning through multiholespinnerets requires that the fluid polymer be carefully filtered toprevent clogging of the minute orifices. In addition the polymerviscosity must be low enough to permit extrusion at practical pressures,and yet high enough so that re-solidification of the polymer in fibrousform will occur with reasonable ease. Polymers of high molecular weight,which generally impart desirable physical properties to fibers such asincreased strength and flexibility, often cannot be spun fromconventional spinnerets since melt or-solution viscosities are often toohigh for extrusion at reasonable pressures. Multi-filament strandsproduced by multi-hole spinnerets have, because of their fineness andconsequent high surface area, greater bulk and covering power and bettertexture than a monofilament strand of equal denier. However, furtherimprovements in these properties cannot be obtained by reduction offilament denier since individual filament diameters less than about 4microns are not ordinarily obtainable. Furthermore, production islimited by the fact that each filament, regardless of size, requires aseparate orifice in the spinneret.

Multi-filament strands consisting of a bundle of parallel filaments areoften difiicult to handle in textile operations because the individualfilaments tend to stray from the main bundle and become entangled withadjacent strands. Contact with surfaces during backwinding or otheroperations interferes with yarn handling. This problem is generally moreserious, the finer the individual filament deniers. Thus, it is oftennecessary to improve the integrity of these strands by twisting or theapplication of a size.

Spray gun, shear precipitation and similar methods form short finerandom length fibers of irregular configuration at higherproductivit-ies and with fewer critical process limitations. Suchfibrous products are suitable for textile use. However, these methods donot without further processing produce textile strands of adequatestrength and uniformity for use in acceptable quality fabrics.

3,081,519 Patented Mar. 19, 1963 It is an object of the presentinvention to provide a novel process for spinning synthetic polymers. Itis another object to provide a process for the production of integral,multi-fibrous, bulky strands directly from fluid polymer. Another objectis to provide a high productivity process for making multi-fibrousstrands of high strength and uniformity. Still another object is theproduction of such products which are processable by convential textile.machines and methods into acceptable quality fabrics. Another object isto provide an integral multi-fibrous yarn-like strand of high surfacearea wherein the fibrous elements are film-like materials defined ingreater detail below and which have a film thickness on the averageunder about 4 microns. A further object is to provide a highproductivity spinning process for the production of a multi-fibrousstrand by extrusion of a fluid polymer from a single orifice wide enoughto obviate fine filtering of the fiuid polymer and to accommodate highviscosity solutions of high molecular weight polymers. Other objects andadvantages will be apparent from the following specifications and theappended claims.

In accordance with the present invention a novel and usefulmulti-fibrous, yarn-like strand is formed by extruding a homogeneoussolution of a fiber-forming polymer in a liquid which is a non-solventfor the polymer below its normal boiling point, at a temperature abovethe normal boiling point of the liquid, and at autogenous pressures orgreater into a medium of lower temperature and substantially lowerpressure. The vaporizing liquid within the extruda-te forms bubbles,breaks through confiningwalls, and cools the extrudate, causing solidpolymer to form therefrom. The resulting multi-fibrous yarnlike strandhas an internal fine structure or morphology which may be characterizedas a three-dimensional integral plexus consisting. of a multitude. ofessentially longitudinally extended interconnecting random lengthfibrous elements, hereafter referred to as film-fibrils; which have theform of thin ribbons of a thickness less than 4 microns. The film-fibrilelements, often found as, aggregates, intermittently unite and separateat irregular intervals called tie points in various'places throughoutthe width, length and thickness of the strand to form an integralthree-dimensional plexus. The film-fibrils are often rolled or foldedabout the principal film-fibril axis, giving the appearance of a fibrousmaterial when examined without magnification. The strand comprising athree-dimensional network of film-fibril elements is hereafter referredto as a plexifilament. The plexifilaments are unitary or integral innature, meaning the strands are one piece of polymer, are continuous innature, and the elements which constitute the strand are cohesivelyinterconnected. Minor physical treatments of the continuous strand suchas shaking, washing, or textile processing will not cause appreciableamounts of the film-like elements to separate from the strand.

Two classes of the plexifilamentary strands are described in detail insubsequent paragraphs. They are (1) a fibrillated strand which is veryfibrous in nature and is an open network of narrow ribbon-like elementsor film-fibrils generally coextensively aligned with the longitudinalaxis of the strand; and (2) a partially condensed strand having thestructure of the fi-brillated strand and containing densified sectionsof film-fibril layers.

The latter class encompasses plexifilamentary strands in any of severalforms termed monotubular, split tubular and ribbon or highly splittubular all described in greater detail below.

A better understanding of the invention may be obtained by reference tothe figures:

FIGURE 1 is a schematic drawing of a. longitudinal microscopic view atabout four power magnification (4x) of a plexifilament consistingpredominantly of filmfibrils 1 having tie points 2 throughout thestrand.

FIGURE 2 is a schematic drawing of longitudinal microscopic view (atabout 250x) of a spread out fibrillated strand.

FIGURE 3 is a drawing of a cross-sectional microscopic view of a portionof the fibrillated structure of FIGURE 1 (about 420x). The film-likenature of the film-fibrils in the fibrillated species is indicated inthe cross-sectional view of FIGURE 3.

FIGURE 4(a) is a schematic drawing of a cross-see tional view (at about4X) of a ribbon strand.

FIGURE 4(b) is a schematic drawing of a cross-sectional view (at about4X) of a monotubular strand.

FIGURE 5 is a drawing showing a fibrillated plexifilament being spun.

FIGURES 6, 7, 8, 9, 10, and 11 are drawings showing cross sectionalviews of spinnerets suitable for use in the practice of the presentinvention.

FIGURE 12 is a graphical representation showing the effect on strandmorphology of initial spinning solution concentration and temperature.

For the purpose of simplifying the visualization of the fibrillatedplexifilament strands, one may suppose that all the morphologicalelements of the plexifilament are derived from bubbles in the viscoussolution which form rapidly as the pressure is reduced during theinitial stage of conversion of fluid polymer to strand. The bubbles thengrow and rupture in various ways to form. the multifibrous network. Theextreme thinness of the pelli-cular material imparts desirable aestheticproperties such as softness and suppleness to plexifilaments and enablesthem to be easily discernible from multi-fibrous strands or coarselyporous fibers of the prior art.

The strands of this invention are continuous in nature and can beproduced in essentially endless lengths. They can be wound on bobbins,or other packages or can be cut into short staple lengths like othertextile strands. The whole strands can have deniers as low as 15 or ashigh as 100,000 or even higher. Preferably, they have deniers between100 and 10,000. They can exist in a condensed moderately fibrillatedform or can exist in a highly fibrillated form. The latter form in heavydeniers has the appearance of silver or tow from extremely fine fibers.The film-fibrils of the present invention, however, are connected in anetwork, there being few if any unconnected fibril ends.

The strands of this invention have tenacities of at least 1.0 g.p.d. andwhen drawn give tenacities as high as 23.0 g.p.d. They were twisted 8t.p.i. before measurement.

All of the strands of this invention are characterized morphologicallyby a three-dimcnsional network of film fibril elements. These networksmay exist in various forms, but in all cases the film-fibrils areextremely thin. On the average the film-fi-bril thickness determined asdescribed below is less than 4 microns thick. In the preferred productsthe film-fibrils are less than two microns thick and may indeed have athickness of less than 1 micron. The film-fibril elements are at leastfive times as wide as they are thick, the actual width being betweenabout 1 micron and about 1000 microns.

The thickness of the film-fibril elements may be determined by use ofthe interferometer microscope. pics are prepared by pressing a strip ofcellophane ad- =hesive tape (Scotch Tape) against the plexifilament. (Inthe case of the monotubular type, the material is cut open first toexpose the film fibrils.) The adhesive Samtape is then pulled away fromthe strand and then has film-fibrils adhering to it. It is dropped intochloroform which dissolves the adhesive material and frees thefilmfibril elements for observing on a microscope slide.

The film-fibril elements in plexifilarnents are found in the form offibril composites which are laminates, aggregates or bundles within thegross strand. Because these fibril composites continuously divide andparts of them join other bundles, it is diificult to count individualfilmfibrils in the strand. However, for convenience, the average numberof fibril composites in a 0.1 mm. thick crosssectional cut of the strandis used as a measure of degree of fibrillation. The number of thesefibril composites per 1,000 denier in a 0.1 mm. length of strand ishereafter referred to as the free fibril count. It is recognized thatthe number of additional film-fibrils which can be pulled away from thefibril composites with slight tension will be many times the numberfound already free, but film-fibrils which adhere to each other are notcounted as separate fibrils in the standard test.

For the purposes of this invention, the free fibril count is determinedby immersing a sample of the strand in water containing a small amountof wetting agent such as Triton X-lOO a product of Rohm and Haas. Thewet sample is frozen using a. bath of liquid nitrogen and is thentransferred to a freezing microtorne where cross sections are cut 0.1'mm. thick. After cutting, each section is dispersed in a drop of wateron a micro-scope slide. After the water has evaporated, the number offragments in each section is counted under a microscope at about 50xmagnification. The average number of fragments per section is used as aquantitative measure for the degree of fibrillation. The test is run onthree sections separated from each other along the length of the strandand the results are averaged. The denier of the strand is determined byweighing a few centimeters of strand. Then the data are reported as freefibrils/ 1000 denier/0.1 mm. length.

FIGURE 2 is an enlarged longitudinal view of a portion of the strand ofFIGURE 1 to show the network structure of plexifilaments. It is planarprojection of the three-dimensional network. The points a represent tiepoints in the structure. The lines 11, 22, 3-3, 44, and 5-5 representthe location of cross-sectional cuts taken in a plane perpendicular tothe paper and to the strand axis. The distance a is the thickness of thecrosssectional out. In the specified free fibril count for thisinvention the distance d is 0.1 mm. In this particular ex-' amplecross-sections A, B, C, and D, will have free fibril counts of 2, 4, 6,and 2, respectively, if the fibrils are not Welded together by thecutting process. Welding is avoided by freezing the strand beforecutting. Preferably more than half of the fibrils have lengths under 1.5cm. (i.e., between points of attachment). The tie points being spatiallyarranged in various planes along the width, length and depth of thestrand are responsible for the three-dimensional structure whichresults.

The predominantly longitudinal orientation of the filmfibrils of allplexifilament strands is readily apparent from the fact that all suchstrands are much more resistant to tearing or breaking transversely thanto splitting length- .ise. The general coextensive alignment of thefibrous elements in the direction parallel to the strand axis is easilydiscernible to the naked eye for most plexifilamentary species.

The plexifilamentary strands of the invention are made of crystallinepolymer. It has been found, quite unexpectedly, that the pellicularmaterial in the as-spun strand when consisting of a crystalline polymeris substantially oriented as measured by electron diffraction, i.e., ithas electron diffraction orientation angles smaller than It is believedthat the high strength of the plexifilamentary strand as spun is closelyrelated to the crystalline orientation within the film-like ribbon andin the structural ar rangement of the fibrils themselves in the strand.In the preferred crystalline oriented products of the invention, thefilm fibrils have electron difiraction angles of less than 55. Theorientation of the crystallites in the film-fibrils is in the generaldirection of the film-fibril axis.

X-ray diffraction patterns which are obtained using the whole strandinstead of just film-fibrils show a substantial amount of orientation inthe strand as spun. The X-ray diffraction orientation angles are lessthan 55 in the preferred embodiments of the invention. The substantialorientation which is exhibited by the .gross strands indicate that notonly are crystallites oriented along the fibrils, but the fibrils arethemselves oriented in the general direction of the strand.

Plexifilament strands have a surface area greater than 2 m. /g., asmeasured by nitrogen adsorption methods. Due to the extremely highpolymer/air interfacial area the strands have marked light scatteringability and high covering power. The surface area of theplexifilamentary strand is determined using essentially the procedureand apparatus described in Faeth, P. A., Willingham, C. B., TechnicalBulletin on the Assembly, Calibration, and Operation of a Gas AdsorptionApparatus for the Measurement of Surface Area, Pore Volume Distribution,and Density of Finely Divided Solids, Mellon Institute of IndustrialResearch, September 1955. In this procedure, the surface area iscalculated from the amount of nitrogen adsorbed by the sample at liquidnitrogen temperature by means of the Bnmauer-Emmet-Teller equation usinga value of 16.2 square angstroms for the cross-sectional area of theadsorbed nitrogen molecule.

An important characteristic of the strands of this invention is thefibrillar texture of the gross strand as observed with the polarizingmicroscope.

In order to observe fibrillar texture, a specimen is prepared asfollows: a short length of strand is frozen in liquid nitrogen and asegment which is 1-5 millimeters long is cut from the frozen strand. Thesegment is placed on its side in immersion oil on a microscopic slide,and the slide is placed in a vacuum chamber and pumped down to removetrapped air. After removing the slide from the vacuum chamber, thespecimen is observed in a polarizing microscope using about 45 Xmagnification. A cover glass is used over the immersed sample. The viewwhich is seen in the microscope is of a longitudinal seg ment of thewhole strand. A first order red plate is used in the microscope and theNicols prisms are crossed at 90 to one another.

A striking color view of the sample is seen'in the polarizingmicroscope. In the strands of this invention long streaks of uniformcolor run parallel to the strand axis. Although there are variety ofcolors, each color extends for long periods along the length of thestrand. An interpretation of the polarized light patterns may be foundin Fiber Microscopy, by A. N. J. Heyn, Interscience Publishers, 1954,pp. 288-352. Monochromatic streaks in color photomicrographs taken withpolarized light are derived from areas of equal optical path differenceand in general will be due to equal orientation and equal thickness inthe strand. These photos demonstrate therefore that thestrands have ahigh degree of organization, and the highly organized areas extend forconsiderable distances along the length of the strand. The strands arecharacterized as fibrillar if at least half of the material making upthe strand appears as monochromatic streaks when observed in thepolarizing microscope. The monochromatic streaks are oriented in thedirection of the strand axis and have an actual (unmagnified) length ofat least 0.2 mm. The monochromatic areas are considered as streaks whenthey have a length at least times the width.

While all of the species of this invention have the strand andfilm-fibril characteristics described in the preceding paragraphs,certain species can be singled out and described in more detail. Themost distinctive of these are the fibrillated strand, the m'onotubularstrand, the split tubular strand and the ribbon strand.

A fibrillated strand is illustrated in FIGURE 1 which is a longitudinalphotomicrograph of the strand at about four-fold magnification. Thisstrand consists of a threedimensional integral plexus of film-fibrilswhich are separated from each other laterally, and extend generally in alongitudinal direction along the length of the strand. The film-fibrilsare interconnected at random intervals in both longitudinal andtransverse directions to provide a three-dimensional network or latticein which all elements are integral with each other. In some instances,it is possible to detect minor amounts of polymeric material presentwhich is not in the form of film-fibrils but rather as small polymermasses and other forms. The quantity of this material is howeverinsignificant and exerts no deleterious effects on the properties of thestrand.

The fibrillated plexifilament is a soft, supple strand having theoutward appearance of a bulky, staple spun yarn. When examined at 400xmagnification, the film fibrils have the appearance of ribbons ofextremely thin pellicular material, folded or rolled approximately aboutthe film-fibril axis. For this reason they appear to be fibrous whenexamined without magnification.

In the most preferred form, the fibrillated strands can be spreadtransversely to many times their original width without Ibreaking anyappreciable number of film-fibril elements. In general, the film-fibrilsseparate when the strand is stretched transversely instead of breaking.The thickness of pellicular material in the cross-section averages lessthan 4 microns.

The free fibril count for the fibrillated species is at least 50 freefibrils/ 1,000 denier/0.1 mm. length and counts of 1,000 or higher areobtained with strands of this species. The strands will however, have aminimum of 25 free fibrils per 0.1 length regardless of denier.

The fibrillated species of this invention is especially preferred forpreparing fabrics with high optical cover and exceptional softness. Forcigarette filters the predominantly fibrillated species is preferredbecause of its very high adsorptive capacity at a filter pressuredifferential of about 3 inches of water. The high surface area alsoprovides these plexifilament strands with high reactivity towardchemical treatments and remarkable adsorption efficiencies inapplications such as in packing material for gas chromatography columns.These advantages of fibrillated plexifilament strands, attributable tohigh interfacial surface area, i.e., a large area of polymer contactingthe atmosphere, are not achieved by conventional fine denier yarns,closed-cell foam yarns or strands having a coarsely porous morphology.

The monotubular embodiment of this invention comprises a tubular strandhaving a film-like outer wall and a fibrous interior. The outer wallwhich is not necessarily cylindrical is a fibrous skin comprising adense laminate of film-fibrils. The fibrous nature of the outer wall canordinarily be demonstrated by examination under a microscope, by workingor by pressing a strip of cellophane adhesive tape against theplexifilament as mentioned above. Within the tubeis a more openfilmfibril network structure whose outer portion, i.e., that partclosest to the tube wall, appears to be partially embedded in, connectedto or a continuation of the plexifilament structure at the inside of thetube wall. Near the film wall on the inside of the tube, thefilm-fibrils are layered together in close association, but near thecenter of the strand, the film-fibrils are in a fairly openconfiguration. In some cases the film-fibrils on the inside of the tubecriss-cross one another to form a diamond pattern, which is readilyvisible when the tube is cut open longitudinally. Often the center ofthe tube is open enough to allow free passage of air through asubstantial length of the strand whenever one applies air pressure as byblowing through the strand. In other instances the material cannot beexpanded by applying air pressure.

7 A probe or dissecting needle simply punctures one of thewalls when anattempt is made to separate the walls.

Despite the embedded nature of the film-fibrils in the monotubularspecies, the structure is nevertheless three dimensional in nature andhas the other characteristics of an integral film fibril plexus. Forexample, this species has a surface greater than 2 m. g. and a filmthickness less than 4 microns. The three-dimensional nature of thefilm-fibril network is obvious in longitudinal views of the fibrousinterior. In addition, it is obvious when filmfibril elements are pulledfrom the inside wall of the structure that the elements are arranged ina three-dimensional network. A cross-sectional view of the monotubularembodiment is shown in FIGURE 4(b). The tube collapses during spinning.The view presents a partially inflated embodiment.

Strands of extremely high strength can be obtained by drawing somemonotubular yarns. These may be knit or woven into fabrics of highstrength. In addition, these strands may be beaten or chopped to producefibrids as defined in Morgan U.S. Patent 2,999,788 with high strength inthe wet-laid form.

The split tubular and highly split tubular or ribbon strands of thisinvention are closely analogous species. Whereas the monotubular strandappears to have a continuous skin or casing, the split tubular strandhas one or more slits in the dense skin running in the machine directionof the strand, thus exposing portions of inner less dense networkmaterial. It is postulated that under spinning conditions more extremethan those employed with the monotubular strand, the solvent vaporescapes at such great velocity as to split the outer skin which for-ms.The split tubular strand has its wall essentially intact. The ribbonstrand, a name descriptive of its shape, presents an outward appearanceof wall fragments of indefinite width and length interspersed withcoarsely fibrillated material when examined under the microscope. It isbelieved to be formed by the complete rupture of a monotubular strandduring spinning. Both of these species can be drawn to obtain strands ofvery high tenacity or can be beaten in an aqueous system to obtainfibrids suitable for use in making synthetic papers.

The continuous strands of this invention are satisfactory for processingon standard textile equipment. Furthermore, these plexifilament strandscan be drawn from 2X to 13 to achieve extremely high tenacities. Forexample, plexifilaments of linear polyethylene drawn about 1l.5 havingachieved tenacities of about 23 grams/ denier; whereas conventionallyproduced fibers of the same polymer do not exceed 13 grams/ denier. Thisstrength level surpasses all other synthetic polymer fibers and clearlypoints out the novelty and remarkable attributes of the presentinvention. Drawing a plexifilament changes its appearance also; itbecomes a lustrous, compact, low bulk structure which has the appearanceof a conventional untextured continuous filament yarn. From this statusit can be worked into a fluffy, high bulk material again, if desired, byblowing air through it or by any other conventional method.

Drawing can be accomplished with the usual means, e.g., hot plate, hotpin, liquid bath, drawing rolls, air jets, etc.

The plexifilaments of this invention may be prepared from syntheticfilament-forming polymers or polymer mixtures which are capable ofhaving appreciable crystallinity and a high rate of crystallization. Apreferred class of polymers is the crystalline, non-polar groupconsisting mainly of crystalline polyhydrocarbons. Common textileadditives such as dyes, pigments, antioxidants, delusterauts, antistaticagents, reinforcing particles, adhesion promoters, removable particles,ion exchange materials, and U.V. stabilizers may be mixed with thepolymer solution prior to extrusion.

Suitable liquids for use in forming the high temperature, high pressurepolymer solutions required for forming the plexifilaments of theinvention should preferably have the following characteristics: (a) aboiiing point at least 25 C. below the melting point of the polymerused; (b) it should be substantially unreactive with the polymer duringextrusion; (c) it should be a solvent for the polymer under thetemperature and pressure conditions suitable in this invention as setforth below; (d) it should dissolve less than 1% of the high polymericmaterial at or below its normal boiling point; and (e) the liquid shouldform a solution which will undergo rapid phase separation (i.e., in lessthan .01 second) upon extrusion forming a non-gel polymer phase, i.e., apolymer phase containing insufiicient residual solvent to plasticize thestructure. In these requirements, the process of the present inventiondiffers radically from conventional solution spinning techniques,wherein the spinning solvent is invariably a solvent for the polymerbelow the normal boiling point ahd generally is a solvent at a roomtemperatures.

Among those liquids which may utilized in the spinning process,depending upon the particular polymer used, are aromatic hydrocarbonssuch as benzene, toluene, etc.; aliphatic hydrocarbons such as butane,pentane, hexane, heptane, octane, and their isomers and homologs;alicyclic hydrocarbons such as cyclohexane; unsaturated hydrocarbons;halogenated hydrocarbons such as methylene chloride, carbontetrachloride, chloroform, ethyl chloride, methyl chloride; alcohols;esters; ethers; ketones; nitriles; amides; fiuorocarbons; sulfurdioxide; carbon disulfide; nitromethane; water; and mixtures of theabove liquids.

Flashing .ofi of solvent during the spinning process of this inventionis similar in some respects to the hash evaporation of solvent in flashdistillation procedures. The rapid and substantial reduction in pressureupon the confined polymer solution when the valve is opened results inthe production of bubbles within the still fluid polymer followed byexpansion of the bubbles and evaporative cooling of the polymer to formpellicular material which ruptures and deforms with resultant productionof the integral plexus of this invention. The initial heat content ofthe spinning solution will affect the final morphology. If the initialheat content is too small, a closed cell morphology will result and ittoo high, a sintered product will be produced. It is surprising thatdespite the violent nature of the process, indefinitely continuousstrands may be obtained.

Certain principals which are helpful in establishing the optimumconditions for preparing products of this invention may be demonstratedby reference to FEGURE 12. This figure is a generalized diagram,descriptive of a large number of polymer/solvent systems, showing theeffect of changes in spinning solution temperature and polymerconcentration on the product morphology. The ordinate of the diagramindicates the initial polymer concentration in weight percent for thesolution, the low polymer concentrations being at the top of the diagramand the high concentrations at the bottom. The abscissa indicates theinitial temperature of the solution in degrees centigrade, the highesttemperatures being toward the right of the diagram. The various areas ofthe figure indicate the type of strand morphology obtained from certaincombinations of temperature and polymer concentration.

Curve I represents the freezing points of a given polymer solvent systemat various concentrations.

Curve 11 represents the critical temperature, Tc, of the solvent C.).The fibrillated species is in general obtained at temperatures above Tc45 indicated by dotted line VII and may be obtained at temperatures evenabove the critical temperature. If nucleating agents are present, thetemperatures which may be employed can be even lower than Tc '45.

Curve V is a boundary representing a concentration of 2% polymer insolution. At concentrations lower than 2% continuous strands aregenerally not obtained. The product obtained from concentrations below2% is usually a discontinuous fibrous mass or a solvent-laden material.

'Curve IV represents a series of borderline conditions. Combinations oftemperature and concentration below curve IV give sintered products,either sintered foams or coarse sintered fibrillar material. Conditionsof concentration and temperature above curve IV give either cellularproducts (area C) or products comprising filmfibrils (area A). 1

Curve VI is a boundary line separating the conditions for makingcellular products and making film-fibril products. In general lowertemperatures and higher polymer concentrations favor the formation ofcellular products. All temperatures on the graph are higher than thenormal boiling point of the solvent.

Area A of FIGURE 12 bounded by lines IV, V, and VI defines the initialconditions of spinning solution temperature and concentration which, inconjunction with other herein described process factors, will producethe plexifilamentary strands of the present invention. The selection ofspecific temperatures and concentrations for spinning a particularpolymer-solvent combination to produce the product of the inventionwould be well within the skill of the art in view of the aforementionedteachings.

It is preferred to use conditions of temperature above the normalmelting point of the 100% pure polymer, and polymer concentrations below30%. For the filbrillated species, it is especially preferred to operateat temperatures within 45 C. of the solvent critical temperature. It hasbeen found that a linear polyethylene-methylene chloride system yieldsthe product of the invention when the polymer concentration on a weightpercent basis is between 2 and 20% and the temperature is above (Tc 45C.) or 193 C.

The solution may also contain dissolved therein, a gas, i.e., asubstance which is normally gaseous under the conditions of temperatureand pressure prevailing on the downstream side of the spinning orifice.Thus, gases such as N CO He, H methane, propane, butane, ethylene,propylene, butene, etc., may be employed. The presence of a dissolvedgas is generally conducive to the production of the highly fibrillatedmorphology. In this connection, the less soluble gases are generallypreferred, i.e., gases which dissolve in the polymer solution underspinning conditions to the extent of less than 7% at saturation based onthe weight of the solution.

It is preferred to operate the extrusion process at velocities whichproduce more than about 3,000 yards of plexifilament per minute. Atthese velocities, an internal orientation force is exerted on thepolymer solution during the brief formative interval in which thepolymer solution undergoes transition first to a system containing vaporbubbles and polymer solution, and thence to a shaped solid; during whichtime critical transient viscosity and velocity gradients exist. Theorientative force facilitates the general longitudinal orientation ofthe fibrils which characterizes plexifilaments.

Plexifilamentary strands can be produced at velocities as high as about17,000 y.p.m. and higher. The extrusion velocity appears to be generallydependent upon the pressure gradient across the orifice, the orificelength and cross-sectional area, solution viscosity, and the geometry ofthe low pressure side of the orifice. The pressure within the extrusionvessel may be increased by using. higher temperatures to obtain higherautogenous pressures, or using pumps, pistons, or inert gases under highpressure. Also, the pressure may be reduced in the region of lowertemperature and pressure into which the solution is extruded.

In general, the fibrillated strands with free fibril count greater than50 fibrils/ 1000 denier/0.1 mm. are produced using spinning conditionsof low polymer concen- 10 tration and/or higher temperatures, orconditions producing high rates of bubble nucleation before the solutionleaves the orifice. High rates of bubble nucleation may be obtained inthe following ways: (1) A dissolved gas,

especially a very slightly soluble one, may be dissolved in the solutionprior to extrusion. (2) A preflashing chamber may be employed, asdescribed in the discussion below of FIGURE 7, wherein a pressureslightly less than the pressure in the heated pressure vessel prevails.(3) Solution temperatures within 45 C. of the critical temperature ofthe liquid may be employed, since at these temperatures the liquidbecomes self-nucleating with respect to bubble production. (4) Finelydivided inert particles may be dispersed in the spinning solution to actas sites of bubble nucleation.

Monotubular plexifilament strands may be obtained in general by spinningfrom spinnerets similar to FIGURES 6 and 10 which have a shroud ortunnel following the spinneret orifice and which do not have twoorifices in tandem. In general the temperatures should be lower and theconcentration should be higher than for producing fibrillated strands.

The ribbon strands are produced by extruding at lower temperatures orpressures or by using higher polymer concentration than with fibrillatedstrands.

The design of the orifice and neighboring structural elements affect thenature of the product obtained. For example, the spinneret device ofFIGURE 7 provides a chamber 5 having an intermediate pressure betweenthe extrusion orifice 8 of the vessel and the actual spinning orifice 3,thereby nucleating or inducing bubble formation. Nucleation gives riseto a high bubble count with subsequent production of highly fibrillatedstructures of relatively low strand deniers. The spinneret assembly inFIGURE 8 contains a venturi insert 7 and is a useful alternate for thespinneret of FIGURE 7. The orifice diameter is generally from 4 toseveral hundred mils. The spinneret of FIGURE 9 having a taper of aboutleading toward the internal end of the orifice and a flare 6 of roughly90 extending about 500 mils outwards from the orifice, is useful forspinning from methylene chloride at temperatures over about C. forproducing high strength strands. The spinnerets of FIGURES 6 and 10,having a downstream shroud or tunnel chamber following the orifice, areconducive to the production of continuous strands having a monotubularconfiguration. Other spinneret and orifice designs may be employed suchas multi-hole spinnerets, spray jets wherein the immediately extrudedstream impinges on a surface which redistributes the stream, swirl jets,slot orifices, annular orifices, and the like. The spinneret of FIGURE11 has the orifice located in a flat downstream surface.

The orifice cross section may be of any simple shape but it is preferredthat the smallest cross-wise dimension be at least about 4 mils,otherwise, unusually high static may be generated during spinning.

The valve in FIGURE 11 is a part of the spinneret assembly and, ifnon-constrictive, does not afiec-t the nature of the product.

The process of the present invention can be carried out batchwise 0rcontinuously. In the case of continuous operation, a solution of polymerin a suitable solvent is heated to the temperature which providesoptimum conditions for the ejection of a plexifilament of the desiredstructure. This solution maybe supplied to an orifice by a meteringpump, thus maintaining a uniform pressure and adequate polymer solutionsupply at the orifice. In such an arrangement, several pressurizedcontainers maybe used to make up the solution. Solutions are alternatelytaken from each of the pressure tanks and discharged through theorifice. Alternatively, polymer and solvents may be mixed continuouslyat any suitable temperature, passed through a heat exchanger, ifnecessary, to attain the desired spinning temperature and then continuously discharged through thespinning orifice. Of

I 1 course, the polymer can be prepared, i.e., polymerized, in thespinning solvent to produce a slurry which, at elevated temperatureswill yield solution of the right composition or concentration. This isdesirable since it simplifies the over-all manufacturing process andthereby affords a considerable economic advantage.

While the plexifilamentary strands of the present invention have beendescribed as three-dimensional network structures, it is possible toobtain webs having only a twodirnensional appearance by a flatteningprocedure. This results, for example, when in the process of preparing afibrillated strand, a bafiie is interposed in the issuing stream a shortdistance from the orifice. The web which can be several times Wider thanthe issuing strand contains the film-fibrils and tie points as before ina threedimen'sional plexus.

Among the numerous utilities for the plexifilaments of this invention,it is especially notewonthy that strong, commercially desirable paperscan he prepared therefrom. Pew shaped structures of synthetic,hydrophobic polymer can be converted on a regular paper-pulping machineinto a slurry which will form satisfactory paper products. The mostserious shortcoming of beaten hydnophobic fibrous polymeric material ofthe prior art has been that the waterleaf formed irom the beaten slurrydoes not possess enough strength to support its own weight; and thismuch strength is necessary to permit the waterleaf to be removed from heinitial water-leaf rforming filter screen for subsequent operations. Itis generally felt that the wet water-leaf, after pressing (or crouching)on the filter screen should have a tenacity of at least about .002 gram/denier to support its own weight during removal from the screen.Plexifilaments converted into pulp on commercial paper-pulping machineryin standard treatment times, produce slurries which will formWaterleaves having more than the necessary 0.002 gram/ denier wet,couched tenacity.

The following examples illustrate specific embodiments of the invention.All parts and percentages are by weight unless otherwise indicated.

In the following examples the pressures which are inclicated may beeither autogenous pressures, i.e., the pressure generated by thesolvent, or may be higher because of the addition of inert gases orbecause of mechanical pressure exerted by la piston or pump. The meltindex of the polymer is the flow in g./10 min, as determined by ASTMMethod D 1238-57T, condition E, and is inversely related to molecularweight. By linear polyethylene is meant polyethylene having a density of0.94 to 0.98 g./=orn. but preferably has a density of 0.95 to 0.97-g./cm. The polymers are of at least film-forming molecular weight.

EXAMPLE I Linear polyethylene (LPE) of melt index 0.50 is mixed withmethylene chloride to produce a mixture containing 7% by weight LPE. Themixture is heated with agitation in a pressure vessel to 210 C. .toproduce a homogeneous solution with an antogenous pressure of about 630psi. The pressure vessel is connected via a -waived transfer line to aspinneret which has a single round orifice with a diameter of 75 milsand a length of 75 mils. Upon suddenly opening the above-mentionedvalve, the solution is ejected and forms a continuous plexiiilamentstrand at a rate of about 5000 y.p.m. The strand as spun has a denier of370, a tenacity of 1.1 -g.p.-d., an elongation of 63% and a modulus of2.1 =g.p.d. The strand is fibrillated and has a fibrillation count of303 free iibrils/1000-denier/01 mm. The fibrils varied in width prom1-50 microns.

EXAMPLE :H

A solution containing 13% linear polyethylene in methylene chloride at195 C. is extruded under 625 psi.

12 through a round orifice of 49 mils in length and 40 mils in diameterwithout any construction ahead of the orifice. Immediately downstreamfrom the onifice is a section flared out at the total angle of extendingtor a dis tance of 0.5 inch. The yarn, obtained at a velocity of about9,000 y.p.m., is a split :t-ube strand comprising an integral,three-dimensional, interconnected assembly of filmdibrils partiallyembedded in a thin ribbon-like matrix and of high as-spun tenacity. Theyarn properties afiter various subsequent operations are given in TableI.

EXAMPLE III A 13% solution of linear polyethylene in methylene chloride,contained in a ten gallon autoclave heated to 196 C. by an externalheating block, and pressured with nitrogen gas, is spun from a spinneretsimilar to that shown in FIGURE 7 wherein the upper orifice 8 is milslong and 60 mils in diameter, the prefla-shing chamher 5 is .36 inchinternal diameter and two inches long, and terminates in an exit orifice3, 40 mils in diameter and 45 mils long. The spinneret differs how'-ever from that of FIGURE 7 in having a 90 flare, 500 mils long followingthe exit orifice, and in having a flat, non-tapered face on the upstreamside of the exit orifice. Several strands are spun using different auto-1 clave pressures. The temperature in the preflashing chamber and theyarn properties for each sample as spun are shown in Table II. Theundrawn strands ane coarsely fibnillated.

Talble II Sample Pros- Temp, Denier Tenacity Elongation Modulus sure C.(g.p.d.) (percent) (g.p.d.)

A 610 192 250 2. 9 83 3. 7 B 620 194 270 3. 0 82 4. 9 C 780 196 260 3 580 4.0

Sample A is drawn 6.7 times in an ethylene glycol bath at 132 "C. at awindup speed of ypm. to produce a drawn yam of 42 denier having atenacity of 19.8 -g.p.d., an elongation of 5.9% and a modulus of 429g.p.d. The drawn strand is lustrous and ribbon-like in form afterdrawing, but dissection reveals a threedimensional filmfi bril networkin the interior of the strand.

EXAMPLE IV Linear copolymers of ethylene and an alpha-olefin were spunfrom 13% solutions in methylene chloride at 200 C. and at about 700 psi.using the .spinnerct of FIGURE 10 having an orifice 60 mils long and 60mils in diameter lfollowed by a cylinder 500 mils by 500 mils. Theribbon stnands were drawn 3.5x in hot ethylene glycol and tested forcreep resistance. The data of Table III indicate that strands preparedfrom copo-lyrners wherein the :comonomer is a 410 carbon alpha-olefinhave better creep resistance than the linear polyethylene homopoly mer.The creep resistance is also seen to improve with decreasing copolymermelt index (increasing molecular weight). in general, the co-monomer mayhave from 3-12 carbon atoms in the molecule.

Table III Comonomer Time 1' or 3 Polymer Melt gram/denier density indexload to break Type Weight glem. strand, hours percent l-butene 2 0. 9420.68 280 Do- 3 0.938 1. 16 101 l-octene 1. 5 0. 944 0. 53 218l-deeene 1. 2 0. 946 0. 054 5, 200 D 5. 0.929 0.09 6, 200 l-dodecene 5.00. 93 1 1. 18 63 Linear polyethylene homopolymer 0 0. 954 1. 7 30EXAMPLE V As-spun, undrawn plexifilament strands prepared from linearpolyethylene using methylene chloride and conditions indicated in TableIV were tested for X-ray diffraction orientation angle by the procedureof H. G. Ingersoll, Fine Structure of Viscose Rayon, Journal of AppliedPhysics (1946), 17, 924. Additionally, for each strand, samples ofpellicular material having an as-spun thickness of about /2 micron werecarefully removed and submitted to electron diffraction orientationangle determination using a Philips 100-A electron microscope, a 100kilovolt electron beam, and a'procedure essentially the same as thatused for the X-ray procedure described above. 'In the following table,the first three products have the tubular morphology, the'fourth andfifth have'lthe split tube morphology and the last three arefibrillated.

Table IV I DEGREE OF ORIENTATION OF VARIOUS LINEAIV POLYETHYLENEPLEXIFILAMENT STRANDS Electron diffraction X-ray Spin- Poly. Spin SpinPoly. orienneret melt temp., press, c0nc., tation Average type index C.p.s.i.g. percent angle, orien- Number deg. tation of deterangle,minations deg.

A 1. 66 207 900 i 21 45 28 12 A 1.60 197 700 16 36 38 14 A l. 52 207 90020 40 48 A 0. 55 206 800 12 42 48 9 A 1. 41 207 900 8 51 51 24 B 1. 25212 720 8 39 24 9 B l. 60 190 600 13 37 44 10 B 1. 50 216 930 12 32 3211 Spinneret A is the spinneret of FIGURE 10, wherein the orifice is'50mils long and 50 mils in diameter, and the cylindrical shroud is 500mils long and 375 mils in internal diameter. Spinneret B is thespinneret of FIG- URE 7, wherein the upper orifice is 125 mils long and75 mils in diameter, the downstream or spinning orifice is 200 mils longand 86 miis in diameter, and the prefiash chamber 5 is 2 inches long and364 mils in internal diameter. As Table IV indicates, both the X-ray andelectron diffraction orientation angles are less than 55". All thestrands tested were soft, strong and well suited for the production ofhigh quality woven or knitted fabrics.

EXAMPLE VI A 13% solution of linear polyethylene in methylene chlorideat 200 C. is saturated with CO at a total equilibrium pressure in thevessel of 1000 p.s.i. The amount of CO dissolved in the solution is3.7%. Before spinning a pressure of 1060 psi. of nitrogen is impressedon the solution, but the solution is not equilibrated with this gas,i.e., the nitrogen does not dissolve to saturation in the solution. Thesolution is then extruded through a simple knife-edge orifice whosediameteris 67 mils. A Well fibri-llated plexifilament strand is obtainedat about 12,000 y.p.m. The strand has a denier of 1120, a tenacity of3.9 g.p.d., an elongation of 78%, a surface area of 8.5 m. g. and anX-ray diffraction orientation angle of about 24. The pcllicular materialaverages less than 2 microns in 14 thickness and has an electrondiiiraction orientation angle of 30. This yarn is eminently suited forthe production of high quality fabrics. Fibril widths ranged from about1-25 microns.

EXAMPLE VII A 13% solution of linear polyethylene in methylene chlorideat 200 C. is saturated with'nitrogen gas at 1915 psi. total pressure.Before spinning, a pressure of 1950 psi. is impressed on the solutionbut equilibrium is not established at that pressure. About 2% ofnitrogen exists dissolved in the solution. The solution is then extrudedthrough a two orifice spinneret as shown in FIGURE 7, the first orificehaving a diameter of 70 mils with a length of 70 mils and the secondorifice being a knife-edge type 67 mils in diameter. The pressurebetween the two orifices is 1490 psi. A monofilament strand or yarn isproduced at a rate of about 8500 y.p.m.

The yarn produced has unusually high bulk and is formed ofrelatively'short and numerous film-fibrils. The free fibril count ofthis yarn is 463/1000-denier/ 0.1 mm. The yarn is equal in manyaesthetic qualities to high quality spun staple yarns or texturizedcontinuous filament yarns. The tenacity is about 1 g./denier and thesurface area is about 9.0 m. gm.

EXAMPLE VIII A 20% solution of a linear polyethylene (1.5 melt index) inmethylene chloride is prepared by stirring at a temperature of 205 C. ina pressure vessel. Stirring is stopped and additional pressure isprovided by introducing nitrogen under pressure to the atmosphere abovethe liquid in the pressure vessel. The total pressure is 800 psi. Aspinneret similar to that shown in FIGURE 10 is used. the spinneret hasa spin orifice of SO-mil diameter with a SO-mil length. The terminalshroud has a diameter of .375 inch and a length of .500 inch. Theas-spun product is a monotubular plexifilament strand comprising ahighlyiluted essentially continuous outer wall with an attached innerfilling comprising an integral, three-dimensional, interconnectingassembly of film-fibrils, the film-fibrils having essentially nounattached'ends. In cross section the outer wall of the tubular strandis deeply crenulated due to partial collapse of the tubular fiormsubsequent to spinning. The tubular strand can, however, be re-inflatedby blowing a gas into a cut end thus indicating that there isconsiderable free space between many of the film-fibrils which form theplexifil-amentary interior of the strand. This plexifilamentary yarnform is ideally suited to an afterastretching treatment to produce verystrong, lustnous yarn such as was made in Example III.

EXAMPLE IX A 16% solution of a linear polyethylene (1.4 melt index) inmethylene chloride is prepared and spun as in Example VIII except that aspin pressure of 700 p.s.i. is used. A plexifilament strand. of outwardtubular form similar to that obtained in Example VIII isobtained;however, in the present case, the tubular form is even less completelyfilled. The inner lining of the tubular strand comprises aninterconnecting, three-dimensional assembly of film-fibrils, thefilm-fibrils being arranged in a unique cross hatched array ininterconnecting layers. A probe can be inserted into a cut end of thepartly hollow tubular strand along its principal axis without causingcohesive tearing of the film-fibril plexus which [forms an integrallining within the outer wall of the tubular strand. The as-spunplexifilament strand has a tenacity of 2. 6 gprd. and an elongation of56%. A wet-process paper made from the product yarn has a tensilestrength of 15.4 lbs./in./oz./yd. an elongation of 56% and an Elmendorftear value of 1 lb./oz./yd.

EXAMPLE X A 16% solution of a linear polyethylene (0.43 melt index). inmethylene chloride is prepared and spun by the method of Example VIIIexcept that the spin temperature is increased to 215 C. The as-spunproduct comprises a plexi-filarnent strand of intact tubular formsimilar to that obtained in Example IV except that the film-fibrilsconstituting the lining of the tubular yarn are substantially parallelto the principal axis of the strand. Also, many of the filnnfibrils orcomposites, continue for inches and even feet before terminating instrong cross-tie connections with other film-fibrils ot theplexifilamentary, integral lining of the tubular strand. The productform of this example is eminently suited to production of strong sheetsvia the wet-paper process route.

EXAMPLE XI A 10% solution of a linear polyethylene (0.58 melt index) inmethylene chloride is prepared and spun according to the method ofExample IX except that the spin temperature is 197 C. A plexifilamentstrand is obtained similar to that of Example X except that the tubularform is split open in a direction more or less parallel to the principalaxis of the strand. The highly folded ribbon-like vestigial outer wallcomprises a plexifilamentary assembly of essentially parallelfilmfibrils embedded in a thin filmy matrix. The as-spun strand has atenacity of 4.3 g.p.d. and an elongation of 61%. The essentiallyfibrillar character of this ribbon strand is readily demonstrated bysubjection of the Strand to an air-jet texturizing treatment which willimpart a highly-fibrillated, open, high-bulk form to the yarn strand.The opened strand comprises a three-dimensional network of film-fibrils.

. EXAMPLE XII A 15% solution of a linear polyethylene (1.3 melt index)in methylene chloride is prepared with a temperature of 223 C. and asuperautogenous pressure of 9-10 p.s.i. The spinneret used is similar tothat shown in FIGURE 7 except that it comprises a series of threeorifices in tandem with the following diameter/length dimensions (mils)for the three orifices, going from the inside of the pressure vessel tothe outside: 86/125, 105/125, and 100/200. Two different sets ofspinning conditions (a) and (b) are used:

Part (a).A spin pressure of 910* p.s.i. is used. A fibrilla-tedplexifilament strand of 790 denier which has a tenacity of 1.2 g.p.d.and a break elongation of 35% is spun out at about 12,300 y.p.m. It hasa fibrillation count of over 200 free fibrils/1000 denier/0.1 mm.

Part (b).-The spin pressure is increased to 1125 p.s.i. and thetemperature is increased to 225 C. A fibrillated strand is spun out atabout 17,000 y.p.m. 'Ihe continuous plexifilament strand possesses asuperfine fibrillation (about five times the fibrillation count of part(a)) is obtained. This soft, pliant high bulk yarn has an enormousspecific surface (12.4 m. /gram) and a very uniform texture and is veryuseful in cigarette filters. The plexifilament yarn has a denier of 690,a tenacity of 1.2 g.p.d. and an elongation of 31%.

EXAMPLE XIII A 15% solution of a linear polyethylene (1.4 melt index) inmethylene chloride is prepared with'a temperature of 218 C. and a totalpressure of 880 p.s.i. A two-orifice spinneret is used similar to thespinneret shown in FIGURE 7 with an attached terminal shroud such as isshown in FIGURE 10. The first orifice of the spinneret has a 75-rnildiameter and a 125-mil length, the second orifice has a l-mil diameterand a 200-mil length and the shroud has a 0.4375 inch diameter and a0.875 inch length. A fibrillated plexifilament strand is obtained with atenacity of 2.7 g.p.d. and an elongation or 46%.

EXAMPLE XIV A 14% solution of a linear polyethylene (0.55 melt index) inmethylene chloride is prepared and spun by the method of Example XI. Theas-spun product is a plexifilament strand in a split tubular form. Theyarn EXAMPLE XV A 5.1% solution of a linear polyethylene (1.6 meltindex) in methylene chloride is prepared and heated to a temperature of217 C. and a total pressure of 900 p.s.i. A spinneret of the type shownin FIG. 8 without insert 7 having an orifice diameter of 125 mils and alength of mils is used. A fibrillated, high bulk plexifilament strand isobtained. A portion of the yarn was tested as a cigarette filter alongwith a commercial filter of 6 d.p.f. cellulose acetate continuousfilament. The data which are recorded in Table V show the superiortar-removing ability of the plexifilamentary filter when the pressuredrop is approximately equivalent to that of the acetate filament filter.The excellent filtering ability of the plexifilament strand isaccomplished with only one fourth as much filter medium as is used inthe acetate fiber filter.

1 Shell method.

EXAMPLE XVI A 12% solution of a linear polyethylene (1.3 melt index) inFreon-11 (trichlorofluoromethane) is prepared and heated to atemperature of 179 C. The pressure vessel is charged with nitrogen underpressure, the dissolved nitrogen content being about 1% and the totalpressure being 900 p.s.i. A spinneret with an orifice of 50 mil diameterand SO-mil length of the type used in Example XV and following thespinneret orifice is a trumpet-like shroud with an entry diameter of0.625 inch, and an exit diameter of 4 inches and with an over-all lengthof 24 inches. The product obtained is a fibrillated, high bulkplexifilament strand Whose component superfine film-fibrils exhibit ahigh degree of crimping or folding along their main axes as aconsequence of the retarding action of the trumpet-shroud. A portion ofthe product yarn was tested in cigarette filter form and compared with acontinuous filament (6 d.p.f.) cellulose acetate filter as shown inTable VI.

Table VI RESULTS OF COMPETITIVE CIGARETTE FILTER TESTING 1 Cambridgemethod, reference, Wartman, W. B., .112, et al.,

Analytical Chemistry, 31 N. 10 1705-9 (1959).

EXAMPLE XVII A 12% solution of a linear polyethylene (0.56 melt ,index)in Freon-l1" (trichlorofluoromethane) is prepared with a temperature of166 C., about 2% of dissolved nitrogen and a total pressure (atspinning) of 1190 p.s.i. The spinneret used is similar to the one shownin FIGURE 10 with a spin orifice of 25-mil diameter and 100-mil lengthfollowed by a shroud of .25 -inch diameter and .500-inch length. A verystrong, predominantly fibrillated plexifilament strand is obtained. 'Inthe as-spun form it has a denier of 205, a tenacity of 4.3 g.p.d. and anelongation of 18% After imparting to the yarn a twist of 8 turns perinch, the yarn has a tenacity of 6 g.p.d. and an elongation of 33%.

EXAMPLE XVIII A 12.4% solution in Freon-l1 of copolymer made from 95%ethylene and octene (0.9 melt index, density 0.9'4g./cm. is prepared ata temperature of 165 C. and a total pressure of 1275 psi. (About'0.5% ofN is dissolved in the solution during its preparation.) The spinneretused is similar to that of FIGURE with the spin orifice having adiameter of 50 mils and a length of 50 mils and with the terminal shroudhaving a diameter of .375 inch with a length of .500 inch. Aplexifilament strand is obtained in a folded ribbon-like form which canbe unfolded to give a ribbon of twice the original width. The product isa ribbon strand. Closer examination of the strand with a microscope at a50-fold to 100-fold magnification shows the strand to consist of anintegral, three-dimensional, interconnecting assembly of film fibrils,some partially embedded and others almost completely embedded in afilm-like matrix, which is a composite or laminar structure offilm-fibril material.

EXAMPLE XIX The procedure of Example I is carried out using a 13.5% byweight linear polyethylene and 86 .5 by weight of a solvent which is amixture of 95 methylene chloride and 5% butane by volume. A spinneretwith an orifice of 75 mils and a length of 75 mils is used. Spinning ofthe solution at a temperature of 200 C. and a pressure of 545 p.s.i.yields a continuous plexifilament strand which is well fibrillated witha fibrillation count of 443 free fibrils/ 1000 denier/0.1 mm. The asspun yarn has a denier of 393.

EXAMPLE XX A 10% solution of polypropylene (0.17 melt index, density0.906) in methylene chloride is prepared and heated to a temperature of223 C., and a pressure of 720 psi. is applied. A spinneret such as shownin FIG- URE 10 is used. The spin orifice has a diameter of 50 mils and alength of 50 mils and the spinneret orifice is followed by a shroud (asshown in FIGURE 10) which has a diameter of 0.375 inch and a length of0.500 inch. A fibrillated plexifilament strand is obtained.

EXAMPLE XXI Various physical mixtures of linear polyethylene withanother-polymer are used to prepare spinning solutions by dissolvingthem in methylene chloride at suitable temperatures and by spinning themas plexifilament strands with certain improved characteristics as shownin Table VII.

' now abandoned.

What is claimed is:

1. A yarn-like strand having a surface areag-reater th an 2 m'. /g.,comprising a three-dimensional integral plexus of synthetic organic,crystalline polymeric,- fibrous elements,'said elements beingcoextensively aligned with the strand axis and having the structuralconfiguration of oriented film-fibrils, an average film thickness ofless than 4 microns and an average electron diifraction orientationangle of lessthan 90. r i p 2. The product, of claim 1 wherein thesurface area is greater than 5" m?/ g.

3. A tobacco smoke filter comprising the product of claim 1.

4. The product of claim 1 wherein the polymeric material ispolyethylene.

5. The product of claim 1 wherein the crystalline polymer is a copolymerof ethylene and a 3-12 carbon alpha olefin.

6. The strand in accordance with claim 1 said strand having an averageX-ray diffraction orientation angle of less than 55.

7. The product of claim 1 wherein the fibrous elements have essentiallyno unattached ends.

8. The strand of claim 1 drawn from 2-13X..

9. The strand of claim 4 which has been drawn and has a tenacity greaterthan 13 grams/ denier.

10. The product of claim 1 having an undrawn, twisted tenacity than 1gram/denier.

11. A fibrillated strand consisting essentially of a threedimensionalintegral plexus of synthetic organic, crystalline polymericfilm-fibrils, said film-fibrils being coextensively aligned with thestrand axis and having an average film thickness of less than 4 microns,and an average electron difiraction axial orientation angle of lesstthan 90, said strand having a surface area of at least 2m. g. and afree fibril count greater than 50 fibrils/ 1000 denier/0.1 mm. and atleast about 25 free fibrils per 0.1 mm. length.

12. The strand of claim 11 wherein the film-fibrils have a width tothickness ratio greater than five.

13. A fibrillated strand consisting essentially of a threedimensionalintegral plexus of crystalline polyhydrocarbon film-fibrils, saidfilm-fibrils being coextensively aligned with the strand axis and havingan average film thickness of less than 4 microns and an average electrondiffraction axial orientation angle of less than 90", said strand havinga surface area of at least 2 m /g. and a free fibril count of at least50 fibrils/ 1000 denier/0.1 mm., and at least 25 free fibrils per 0.1mm. length.

1-4. The strand of claim 13 wherein the crystalline hydrocarbon islinear polyethylene.

15. A partially condensed strand of synthetic organic, crystallinepolymer, said strand having a surface area of at least 2 m g. and saidstrand consisting essentially of a three-dimensional integral plexus offilm-fibrils which Table VII PLEXIFILAMENT STRANDS MADE FROM POLYMERBLENDS Spin temp., Polymer blend Percent poly- O./spin Productdescription mer in solution press p.s.1.g.

Pol eth lene 9O 01 st ene 10 10 plus 0.27 220/1 050 Predominantlyfibrillated strand bulkier and more resilient y y p y w dissolved 1:than that from polyethylene alnne. Polyethylene, basic dyeablepolyester, 1 15% 16 207/700 Split tubular yarn of excellent dyeability.Polyethylene, 50%; polyoxymethylene, 50% 12 217/1, 050 Predominantlyfibrillated tough yarn. Linear polyethylene, 50%; branched polyethylene,50%- 12 21011.050 Hgggflg flbnllated, res1lient yarn with microcnmp infilm- 1 The condensation product of ethylene glycol with a 98/2 molarmixture of terephthalic/5- (sodium sulio)'isophthalie acid.

are coextensively aligned with the strand axis and having an averagefilm thickness of less than 4 microns, and an average electrondiffraction axial orientation angle of less than 90 and densifiedsections of film-fibril layers.

16. The strand of claim 15 wherein the polymer is a crystallinepolyhydrocarbon.

17. The strand of claim 15 wherein the polymer is lin ear polyethylene.

18. The strand of claim 15 wherein the densified regions are in the formof tubular outer wall.

19. The strand of claim 15 wherein the densified regions are in the formof a split tohular outer wall.

20. The strand of claim 15 wherein the densified regions are in the formof Wall fragments.

21. A strand comprising a three-dimensional integral plexus of"synthetic organic crystalline polymeric filmfibril elements which arecoextensively aligned with the strand axis, said film-fibril elementshaving a thickness References Cited in the file of this patent UNITEDSTATES PATENTS 2,268,160 Miles Dec. 30, 1941 2,372,695 Taylor Apr. 3,1945 2,853,741 Costa et a1. Sept. 30, 1958 2,920,349 White Jan. 12, 1960FOREIGN PATENTS 1,176,856 France Nov. 24, 1958 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3 O81 519 March 19 1963Herbert Blades et 8.1..

It is hereby certified that error appears in the above numbered patentreqliring correction and that the said Letters Patent should read ascorrected below.

Column 11, line 57, for "7%" read 10% 0 Signed and sealed this 16th dayof June 1964a (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Alli-sling Officer Commissioner ofPatents

1. A YARN-LIKE HAVING A SURFACE AREA GREATER THAN 2 M.2/G., COMPRISING ATHREE-DIMENSIONAL INTEGRAL PLEXUS OF SYNTHETIC ORGANIC, CRYSTALLINEPOLYMERIC, FIBROUS ELEMENTS, SAID ELEMENTS BEING COEXTENSIVELY ALIGNEDWITH THE STRAND AXIS AND HAVING THE STRUCTURAL CONFIGURATION OF